EP4148300A1 - Method for protecting a differential - Google Patents

Abstract

A method for protecting a differential (1) of a motor vehicle, with the differential (1) dividing a drive torque between two outputs, with at least one temperature (T _KP , T _G ) on the differential (1) being continuously measured from a temperature model (TM) is calculated, wherein if the calculated temperature (T _KP , T _G ) exceeds a specified limit value, the drive torque is lowered.

Description

field of invention

The present invention relates to a method for protecting a differential of a motor vehicle.

State of the art

Differential gears, or "differentials" for short, are known to be used in motor vehicles in order to split a drive torque between two outputs, for example left and right semi-axles of a front or rear axle of the motor vehicle as a so-called "axle differential". Such differentials can be designed "open", that is, consistently allow a speed difference between the two outputs, or be designed as a locking differential, so that the speeds of the two outputs are fully or partially coupled to each other.

It is known that open differentials can be damaged if the rotational speed is too high, so that a rotational speed protection device can be used for this purpose, which intervenes when the rotational speed is too high at an output of the differential.

Summary of the Invention

It is an object of the invention to specify a method for protecting a differential of a motor vehicle that provides reliable protection of the differential against overload and can also be used for a limited-slip differential.

The object is achieved by a method for protecting a differential of a motor vehicle, with a drive torque being divided between two drives by the differential, with at least one temperature at the differential being continuously calculated from a temperature model, with the case that if the calculated temperature exceeds a specified limit value, the drive torque is reduced.

According to the invention, the current load on the differential is constantly determined by a calculation based on a temperature model. For the calculation based on this model, the required input parameters are continuously determined, in particular using sensors. According to the invention, the temperature at the differential is thus taken into account on the basis of the calculation model in order to determine the stress on the differential due to high temperatures and, if necessary, to reduce the drive torque at the differential.

The method is preferably carried out by a control device, in particular by a transmission controller.

The drive torque can be lowered in particular by reducing an engine torque and/or by switching on all-wheel drive of the motor vehicle and/or by applying the brakes and/or by switching on an electrically driven axle.

The differential is preferably a locking differential.

The differential is preferably an axle differential.

The continuous calculation of at least one temperature at the differential from a temperature model preferably includes the continuous calculation of a temperature at a frictional contact between differential gear wheels, in particular planet wheels, and the housing of the differential.

The continuous calculation of at least one temperature at the differential from a temperature model preferably includes the continuous calculation of a temperature at the housing of the differential.

Particularly preferably, the continuous calculation of at least one temperature on the differential includes both of the areas mentioned, namely a frictional contact of differential gears, in particular planetary gears, to the housing, and also on the housing itself.

The temperature model preferably constantly calculates the temperature on the housing of the differential and on the frictional contact of the planet gears with the housing. The frictional contact between housing and planet is a critical point. The frictional contact between the planet and the case is a local point of low mass, while the case has a large mass. When energy is input, the temperature at the critical point rises much faster than at the housing. The critical point cools down more quickly the greater the difference in temperature between the critical point and the housing. The housing then usually transfers the energy to an oil and/or the rest of the transmission system. A dependence on a sump oil temperature, rotational speed of the output, and the volume flow of a cooling pump for the cooling behavior can be taken into account by the temperature model.

If the temperature exceeds a predefined threshold, the drive torque is reduced so that only a small amount of power is fed into the differential. The differential cools down and is protected from heat damage (scuffing / pitting).

The reaction to the calculated temperature, in particular the torque reduction or torque increase, can also take place as a function of the incline, that is to say it can take into account the current negotiation of an incline.

The current calculation of the temperature at a frictional contact of differential gears, in particular planetary gears, with the housing of the differential is preferably carried out as a function of the last calculated temperature at the housing of the differential.

In addition, the current calculation of the temperature at the housing of the differential is preferably carried out as a function of the last calculated temperature at a frictional contact of differential gears, in particular planetary gears, with the housing of the differential.

The calculations of the temperature at the frictional contact of planetary gears to the housing on the one hand and at the housing itself on the other hand are preferably made dependent on one another, so that the results of the respective calculation are included in the next calculation of the other temperature variable.

In addition, at least one power output at the differential is preferably calculated continuously from a power model, with the drive torque being reduced if the calculated power exceeds a limit value, so that in this case only a small power input into the differential is done. The limit value can depend on the incline of the roadway, that is to say the incline of the roadway, and the duration.

The limit values of the power calculation can depend on the incline, since the axle load distribution is different when driving up an incline and, accordingly, so is the possible torque that can be sold and the build-up behavior of the differential speed.

The limit values of the power calculation can be time-dependent and dependent on the incline, since the axle load distribution is different when driving up an incline and accordingly the bodywork behavior, in particular the gradient of the differential speed.

The reaction to the calculated power, in particular the gradient of the torque reduction, can also be dependent on the incline, i.e. dependent on information about the current driving up an incline, since the axle load distribution is different when driving up an incline and therefore also the possible torque that can be sold.

The gradient of the reaction, both the torque reduction and the torque increase, on the calculated power and the temperature model is preferably dependent on the currently transmittable torque and the target torque of the reaction (delta torque) and the currently applied load level (stress level). The delta torque is the current deliverable torque minus the target torque.

A characteristics map for the gradient of the torque reduction and/or gradient of the torque increase is preferably used, the x-axis of which is formed by the delta torque and the y-axis of the stress level (degree of stress) is formed. This gradient is preferably multiplied by a factor depending on the slope. The advantage of this calculation is that due to the indirect dependency on the coefficient of friction of the road surface and the stress level, the moment can be optimally distributed, resulting in better driving behavior (more comfortable, sportier) and better performance of the vehicle.

At least one differential speed at the differential is preferably also continuously monitored, with the drive torque being reduced if the differential speed exceeds a specified limit value. The speed path can be another parallel branch of the monitoring. If a speed threshold is exceeded, the engine torque is preferably reduced independently of the temperature model and the power model.

Preferably, if the drive torque is to be reduced, information about the current roadway gradient, ie the gradient of the roadway, is determined and the gradient of the reduction in the drive torque is determined as a function of the roadway gradient determined. An increase in the drive torque, specifically the gradient of the torque increase, in particular after a previous reduction in the drive torque, can also be determined as a function of the current gradient of the road, ie as a function of the current driving on an incline.

If the drive torque is to be reduced, the drive torque is preferably reduced as a function of whether the motor vehicle is currently in all-wheel drive mode. In all-wheel drive, part of the torque (currently set all-wheel drive torque) is sent to the other axle (e.g. rear axle) and thus not through the differential, whereby less energy is introduced at the differential and the limits of the protective function are not reached or are reached later. The consequences of the lower energy input are better drivability or better system behavior as a result of fewer, reduced control interventions and better component protection.

Brief description of the drawings

Fig. 1a

ist eine Schnittansicht eines Differentials, für das ein erfindungsgemäßes Verfahren zum Schutz des Differentials durchgeführt werden kann.

Fig. 1b

ist eine seitliche Darstellung des Differential gemäß Fig. 1a, ohne Gehäuse.

Fig. 1c

ist eine Darstellung des Differential gemäß Fig. 1a von vorne.

Fig. 1d

ist eine Explosionsdarstellung des Differential gemäß Fig. 1a.

Fig. 2a

ist eine Darstellung des Differentials gemäß Fig. 1c von vorne und zeigt die Position des Ausschnitts Fig. 2b.

Fig. 2b

zeigt den Ausschnitt gemäß Fig. 2a.

Fig. 3

ist eine schematische Darstellung eines erfindungsgemäßen Verfahrens zum Schutz eines Differentials.

The invention is described below by way of example with reference to the drawings.

Fig. 1a

Fig. 12 is a sectional view of a differential to which a differential protection method according to the present invention can be applied.

Fig. 1b

is a side view of the differential according to Fig. 1a , without housing.

1c

is a representation of the differential according to Fig. 1a from the front.

Fig. 1d

is an exploded view of the differential according to Fig. 1a .

Figure 2a

is a representation of the differential according to 1c from the front and shows the position of the cutout Figure 2b .

Figure 2b

shows the section according to Figure 2a .

3

Figure 12 is a schematic representation of a method of protecting a differential according to the invention.

Detailed description of the invention

In the Figures 1a to 1d a differential 1 is shown as an example for which a method according to the invention for protecting the differential can be carried out.

The differential 1 allows a drive torque to be divided between two outputs. The drive torque can be introduced via the housing 2 of the differential, which also forms the planet carrier for the planet gears 3 . The drive torque is transmitted to two side wheels 5 via the planet wheels 3 and is optionally transmitted from the side wheels 5 via two associated clutches 6 to half axles arranged on the left and right (not shown in Fig Figures 1a to 1d ), which can rotate radially within the housing 2 with its cover 4. Axially between the clutches 6 and the housing 2 or the cover 4 and between the side gears 5 are thrust washers 7, for example made of metal or metal-polymer.

The 2 shows the areas on differential 1 that are relevant for the continuous calculation of temperatures T _KP , T _G on differential 1 from a temperature model TM Figure 2a a possible position of the cutout Figure 2b in a front view of the differential, accordingly 1c .

On the one hand, the temperature is determined at the "critical point" KP, which is a point where frictional heat occurs directly between the rotating planet gears 3 and the housing 2 represents. In addition, the temperature at a point G in the housing 2 of the differential 1 is determined.

The critical temperature at the critical point KP is therefore the temperature at the frictional contact between the planet gears 3 and the housing 2. A temperature rise primarily occurs there. Due to the frictional power at the frictional contact, energy is introduced, which leads to an increase in temperature. This temperature is cooled down at the critical point KP in that the heat or energy is dissipated to the housing 2, for example at point G of the housing 2, with its comparatively large mass.

3 shows a schematic of a method according to the invention for protecting a differential 1. A load S on the differential 1 can be calculated in various ways, namely on the one hand on the basis of the temperature T, by calculating temperature entries at the critical point T _KP and on the housing T _G with the aid of a temperature model TM, which lead to a load due to temperature S _T at the critical point KP. In parallel with this, the load S on the differential 1 can be determined on the basis of the power P with the aid of a power calculation PB of the power P dropping on the differential 1 and the associated load through power Sp.

If the calculated load S on the differential 1 exceeds a predetermined limit value, a suitable reaction can take place, namely ultimately a reduction in the drive torque on the differential 1, which can take place by directly reducing the torque of a drive motor RM and/or by switching on all-wheel drive RA and/or or by a braking intervention RB and/or by switching on an electrically driven axle. The electric axle generates propulsion similar to a conventional all-wheel drive. The additional propulsion means that more torque can be transmitted to the front axle with a lower differential speed at the same time.

Regardless of the calculation of the load S based on the temperature T and the power P, the same reactions, namely reducing the torque RM of a drive motor and/or switching on all-wheel drive RA and/or by switching on an electrically driven axle and/or braking intervention RB also take place or be influenced on the basis of tracking the speeds N at the differential, namely by determining a load due to the speed difference ΔN at the differential 1 in relation to the current drive torque M at the differential 1.

In detail, the temperature at the critical point T _KP can be calculated by the temperature model using the following equation:

• T_KP(n) die Temperatur am kritischen Punkt KP zum Zeitpunkt n T_KP(n-1) die Temperatur am kritischen Punkt KP zum vorausliegenden Zeitpunkt n-1
• T_G(n-1) die Temperatur am Gehäuse G zum vorausliegenden Zeitpunkt n-1
• M das Drehmoment, welches durch das Differential geleitet wird
• C1 ein konstanter Faktor
• ΔN die Differenzdrehzahl (an der Achse vom Differential)
• LE% der Sperrwert
• AF ein Anteilfaktor der ein erstes Kennfeld, nämlich Differenzdrehzahl über Drehmoment berücksichtigt und ein zweites Kennfeld, nämlich Temperatur am kritischen Punkt über Sumpföltemperatur. Die Ergebnisse aus dem ersten Kennfeld und dem zweiten Kennfeld werden multipliziert.
• X0 eine Konstante (thermische Masse im kritischen Punkt)
• Δt die Zeitdifferenz zwischen Zeitpunkt n und Zeitpunkt n-1

where:

• T _KP (n) the temperature at the critical point KP at time n T _KP (n-1) the temperature at the critical point KP at the preceding time n-1
• T _G (n-1) the temperature at the housing G at the previous point in time n-1
• M is the torque that is passed through the differential
• C1 a constant factor
• ΔN the differential speed (on the axle of the differential)
• LE% the lock value
• AF is a proportion factor that takes into account a first map, namely the differential speed over torque, and a second map, namely the temperature at the critical point over the sump oil temperature. The results from the first map and the second map are multiplied.
• X0 a constant (thermal mass at the critical point)
• Δt is the time difference between time n and time n-1

The temperature T _G on the housing G, 2 can experience a temperature rise, with the heat or energy being dissipated from the frictional contact point KP “quickly” into the housing G due to the large mass on the housing G. In the process, the temperature T _G of the housing increases. The temperature T _G at the housing G,2 is reduced by transferring heat/energy to the rest of the system through the large surface area of the housing G,2.

The temperature T _G on the housing can be calculated using the formula:

• T_G(n) die Temperatur am Gehäuse G zum Zeitpunkt n
• T_G(n-1) die Temperatur am Gehäuse G zum vorausliegenden Zeitpunkt n-1
• T_KP(n-1) die Temperatur am kritischen Punkt KP zum vorausliegenden Zeitpunkt n-1
• T_O(n-1) die Ölsumpftemperatur zum vorausliegenden Zeitpunkt n-1
• N_RG die Drehzahl am Ringrad
• ΔN die Differenzdrehzahl
• CCP_Vol der Kühlölvolumenstrom
• F(N_RG;ΔN;CCP_Vol) ein Wert aus einem Kennfeld mit den Achsen Drehzahl am Ringrad, Differenzdrehzahl der multipliziert wird mit dem Kühlölvolumenstrom.
• Die Drehzahl am Ringrad N_RG hat einen direkten Einfluss auf das Abkühlverhalten, nämlich die Abkühlgeschwindigkeit.
• C2 ist ein konstanter Faktor
• T_Oil die Ölsumpftemperatur

where:

• T _G (n) the temperature at housing G at time n
• T _G (n-1) the temperature at the housing G at the previous point in time n-1
• T _KP (n-1) the temperature at the critical point KP at the time n-1 ahead
• T _O (n-1) the oil sump temperature at the previous point in time n-1
• N _RG the speed at the ring gear
• ΔN the differential speed
• CCP_Vol the cooling oil volume flow
• F(N _RG ;ΔN;CCP_Vol) a value from a map with the axes speed at the ring wheel, differential speed which is multiplied by the cooling oil volume flow.
• The speed at the ring gear N _RG has a direct influence on the cooling behavior, namely the cooling speed.
• C2 is a constant factor
• T _Oil the oil sump temperature

The power P can be calculated using the following equation: $$\mathrm{P}\left(\mathrm{t}\right)={\mathrm{Tq}}_{\mathrm{choose}}\left(\mathrm{t}\right)*\Delta \mathrm{N}\left(\mathrm{t}\right)*\mathrm{TBR}\left(\%\right)$$

• Tq_wh1 das Drehmoment an den angetriebenen Rädern durch das Differential
• TBR(%) die Torque Bias Ratio
• ΔN die Differenzdrehzahl
• Jeweils zu einem Zeitpunkt t.

where:

• Tq _wh1 is the torque at the driven wheels through the differential
• TBR(%) is the torque bias ratio
• ΔN the differential speed
• At a point in time t.

The following applies to the speed calculation N: the speed path N is independent of the line and temperature path P, T or generally of the determination of the load S. For example, with an active load S and a very high differential speed ΔN, the torque is further reduced by the speed protection by Reducing the torque RM of a drive motor and/or switching on all-wheel drive RA and/or braking intervention RB.

The determination on the speed path N is based on the determination of a characteristic value from a characteristic map, namely the speed difference over the torque ΔN/M. Above a specific threshold of the differential speed ΔN, the engine torque is preferably reduced by a factor RM. When the differential speed ΔN is reduced, the torque is increased again in line with the map ΔN/M.

In general, different limit values for the load S and reactions of different strengths, namely reducing the torque RM of a drive motor and/or switching on all-wheel drive RA and/or braking intervention RB, can be set depending on the current incline, i.e. the incline of the road.

Reference List

1

differential

2

Housing

3

planet wheel

4

cover

5

side wheel

6

coupling

7

thrust washer

T

temperature

TM

temperature model

CPM

temperature at the critical point

TG

temperature in the housing

P

Performance

PB

power calculation

N

number of revolutions

ΔN

differential speed

M

drive torque

S

Burden

ST

exposure to temperature

Sp

performance load

rm

Reducing the torque of a drive motor

RA

Activation of all-wheel drive

RB

braking intervention

Claims (9)

Method for protecting a differential (1) of a motor vehicle, wherein a drive torque is divided between two drives by the differential (1),
characterized in that at least one temperature (T _KP , T _G ) on the differential (1) is continuously calculated from a temperature model (TM), with the drive torque being reduced if the calculated temperature (T _KP , T _G ) exceeds a specified limit value . Method according to claim 1,
characterized in that the continuous calculation of at least one temperature (T _KP , T _G ) on the differential (1) from a temperature model (TM) the continuous calculation of a temperature (T _KP ) on a frictional contact of differential gears, in particular of planet gears (3 ), To the housing (2) of the differential (1). Method according to at least one of the preceding claims, characterized in that the continuous calculation of at least one temperature (T _KP , T _G ) on the differential (1) from a temperature model (TM) the continuous calculation of a temperature (T _G ) on the housing (2) of the differential (1). Method according to claim 2 and claim 3,
characterized in that the current calculation of the temperature (T _KP ) at a frictional contact of differential gears, in particular planetary gears (3), to the housing (2) of the differential (1), depending on the last calculated temperature (T _G ) am Housing (2) of the differential (1) is carried out, and / or that the current calculation of the temperature (T _G ) on the housing (2) of the differential (1), depending on the last calculated temperature (T _KP ) at a friction contact of Differential gears, in particular planetary gears (3), to the housing (2) of the differential (1) is carried out. Method according to at least one of the preceding claims, characterized in that at least one power (P) at the differential (1) is continuously calculated from a power model (PM), with the drive torque being reduced if the calculated power (P) exceeds a limit value, the limit value being dependent on the slope and/or time. Method according to at least one of the preceding claims, characterized in that at least one differential speed (ΔN) on the differential (1) is continuously monitored, with the drive torque being reduced if the differential speed (ΔN) exceeds a specified limit value. Method according to at least one of the preceding claims, characterized in that the drive torque is reduced by reducing the torque of a drive motor RM and/or by switching on all-wheel drive RA and/or by switching on an electrically driven axle and/or by braking intervention RB. Method according to at least one of the preceding claims, characterized in that if the drive torque is to be reduced, information about the current roadway gradient is determined and the drive torque is reduced as a function of the determined roadway gradient. Method according to at least one of the preceding claims, characterized in that if the drive torque is to be reduced, the drive torque is reduced as a function of whether the motor vehicle is currently in all-wheel drive mode.

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